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The present invention relates to electrical circuits that provide power to a load in a multi-phase manner. These types of circuits are referred to as DC to DC converters or buck converters or step-down converters. These switching circuits may be used in a number of different environments, including providing power to microprocessors.
As integrated circuits become more complex and operate at higher levels of performance, maintaining the power source to the integrated circuit (IC) within required operating ranges becomes increasingly difficult. Several of the problems associated with supplying power to modern ICs are described as follows.
The main problem associated with supplying power to modern ICs is voltage regulation. The modern trend is for smaller and smaller voltage supply levels. In modern electronic systems, high performance ICs such as microprocessors may require a different voltage level than other circuits within the system. The common solution is to provide an external voltage converter or regulator near the high performance IC to supply the required voltage so that the rest of the system may be supplied with a standard voltage.
The circuit of FIG. 1 shows a conventional DC-to-DC power converter that is widely used to supply power to electronic devices, such as in computers, printers, and other devices. Such DC-to-DC converters are available in a variety of configurations for producing the desired output voltage from a source voltage. For example, a step down converter produces an output voltage that is less than the source voltage. A typical step down converter includes one or more power switches which are pulse width modulated to connect the source voltage to an output inductor to thereby power the load. The converter includes a gate driver for the high side switch, and a high speed peak current control loop. A portion of the converter""s DC output is applied to a transconductance error amplifier that compares the fed back signal with an internal reference voltage. The feedback signal is generated by a resistor divider connected across the output of the converter.
The transconductance error amplifier compares the DC level of the fed back voltage with an internal reference, while providing voltage loop compensation using external resistors and capacitors. A signal proportional to the output inductor""s current may be used to limit component stress during output overloads (overload protection). However, a regulation application needs a higher fidelity current signal than the overload protection application. Typically the heat sinks and thermal design of the DC-to-DC converter are sized for efficiency, and the worst case variation of the overload trip level (current signal) still maintains the components below their maximum ratings.
There are several methods of controlling the regulation of the output voltage. These methods are commonly known as voltage mode control, peak current mode control, and other various methods. Another one of these methods is average current mode control. The embodiment of this invention shown in FIG. 1 utilizes average current mode control.
Perhaps the most common approach to sensing the output inductor current in a step own converter uses a sensing resistor connected in series with the output inductor. The circuit reconstructs the output inductor current as a differential voltage across the sensing resistor. Most IC""s using this approach regulate the output voltage with current mode control and use the signal for output voltage feedback.
Multiphase converters have also been employed in the DCxe2x80x94DC converter topologies. For example, a dual interleaved DCxe2x80x94DC converter uses two buck converters in parallel. However, these two converters are switched 180 degrees out of phase with each other. There are several advantages associated with multiphase converters. They include reduced output voltage ripple and reduced input current ripple. Therefore multiphase converters are commonly used for supplying high performance CPU power.
The conventional multi-phase circuits as described are capable of monitoring individual phase currents and provide automatic duty cycle adjustment to keep the inductor currents in the interleaved DC to DC switching circuits balanced. The prior art circuits fail however, to teach any means or method of detecting a phase failure within the system. It is common that one phase of a multi-phase system may fail and go undetected, as power may still be supplied by the other working phases. Therefore a solution is required that takes into account all the above mentioned problems and limitations associated with providing power to IC chips.
The drawback of the conventional interleaved DC to DC switching circuits is that they are incapable of detecting when one of the phases has failed. Often while in operation, a single phase within a multi-phase system will fail. It is common that even with a failed phase, the working phases will still provide power to the load. These undetected phase failures cause regulators to operate under high stress conditions as they must carry additional current normally provided by the failed phase. It should be noted that while the current is higher than usual, the voltage tends to stay within appropriate bounds thereby masking the phase failure. The high stress operation of the regulators causes faulty circuit operation and usually component malfunction or destruction. The present invention offers a low cost, reliable, on chip implementation that takes advantage of the nature of the average current mode topology to detect phase failures within a multi-phase system.